This invention relates to wideband communications and more particularly to minimizing the effects of interference in a radio receiver system utilizing an adaptive antenna array.
Any communication system is susceptible to degradation due to interfering conditions. In a wideband transmission system the desired signal is vulnerable to interruption by natural phenomena, interference from other signals, or countermeasures. Countermeasures may take the form of a variety of jamming schemes whose sole purpose is to disrupt the operation of a receiver.
A variety of techniques are currently used to decrease the effects of interference in receivers. Frequency agility, sensitivity time control, sidelobe blanking, random PRF and sidelobe cancellation are but a few of the well known techniques for countering interfering signals. Jammer signals are often non-pulsed or continuous wave and may be sinusoidal, modulated or noise like in nature.
However, in some environments such as GPS, (Global Positioning System), many of the common methods used for cancellation of interfering signals are not applicable. A GPS receiver requires the reception of numerous signals to derive a location from satellites at random locations. Adaptive nulling is an often used technique for rejecting interference. Adaptive nulling rejects interference by effectively reducing the directional sensitivity of the receiver antenna in the direction of the interfering signal. A well known approach to perform adaptive nulling is predicted upon the use of circuitry between the antenna and receiver that in essence nulls the undesired signal by accomplishing weighting functions of the received signal. Use of such weighting functions allows one the opportunity to process the received signal prior to routing it to the receiver so that the receiver only "sees" the desired carrier signal.
Common technical implementations of the weighting function circuitry include the use of a circuit card assembly populated with numerous discrete devices such as amplifiers, mixers and PIN diodes. Each antenna element has a dedicated network of components that controls the attenuation and phase of the received signal. Use of the above described implementation has numerous drawbacks, including but not limited to, increased power and space requirements, premature failure, cost, and operating speed.
Accordingly, a need exists for an improved apparatus and method of accomplishing spatial nulling utilizing antenna control electronics.